CHROMATING METHOD EXCELLENT IN PREVENTION OF YELLOW POWDER AND CHROMATING LIQUID

摘要

PURPOSE: To provide a chromating method and a chromating liquid excellent in prevention of yellow powder. ;CONSTITUTION: A chromating liquid is applied by direct coating on a galvanized sheet having a plating layer containing total ≤0.1% of Pb, Sb and Sn. The chromating liquid is prepared by adding 3-20g/l phosphoric acid, 0.2-3g/l fluorine compd., and 4-180g/l colloidal silica (calcumated as SiO₂) to a partilly reduced chromic acid having 2-30g/l Cr concn. and 0.1-0.7 reduction ratio of Cr³⁺/(Cr³⁺+ Cr⁶⁺). Then the coated sheet is heated and dried to form a achromate film having 5-90mg/m² Cr amt. on the surface. This method has such an effect to surely prevent production of yellow powder after chromate treatment.;COPYRIGHT: (C)1993,JPO&Japio